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United States Patent |
5,588,210
|
Lederman
|
December 31, 1996
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Method of manufacturing a unitized seal
Abstract
A simplified method of manufacturing and assembling a unitized seal uses
only three basic components, and no steps involving direct molding of
elastomer to casings, or gluing or otherwise securing elastomer to the
casings. Two simple, inner and outer casings have axially opposed,
radially overlapping annular webs, and radially opposed, oppositely
axially extending seal walls. An integral seal unit has coplanar, inner
and outer disks joined at a frangible central seam. Each disk has a pair
of converging seal lips disposed symmetrically to either sid of a
respective seal wall. When the unit is squeezed axially between the
casings during assembly, the seal walls enter between the seal lips,
bottom out on the disks, break the seam, and embed the disks automatically
into the casings, with no other assembly steps needed.
Inventors:
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Lederman; Frederick E. (Sandusky, OH)
|
Assignee:
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General Motors Corporation (Detroit, MI)
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Appl. No.:
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286362 |
Filed:
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August 5, 1994 |
Current U.S. Class: |
29/898; 29/413; 29/432; 264/163 |
Intern'l Class: |
B29C 045/08 |
Field of Search: |
264/138,238,163
29/898,888.3,413,432
|
References Cited
U.S. Patent Documents
3101954 | Aug., 1963 | Huddle | 277/39.
|
4822183 | Apr., 1989 | Lederman | 384/607.
|
5046229 | Sep., 1991 | Lederman | 29/418.
|
5046248 | Sep., 1991 | Lederman | 29/898.
|
5201533 | Apr., 1993 | Lederman | 277/152.
|
5326523 | Jul., 1994 | Gustavel et al. | 264/163.
|
5346662 | Sep., 1994 | Black et al. | 264/138.
|
5472334 | Dec., 1995 | Takahashi | 264/163.
|
5502547 | Mar., 1996 | Shirai | 355/215.
|
Foreign Patent Documents |
1070221 | Apr., 1986 | JP | 264/163.
|
Other References
Document Number 08/245126 Name Lederman Filing Date 17-May-1994.
Document Number 08/247202 Name Lederman Filing Date 20-May-1994.
Document Number 08/250,878 Name Lederman Filing Date 31-May-1994.
|
Primary Examiner: Cuda; Irene
Assistant Examiner: Butler; Marc W.
Attorney, Agent or Firm: Griffin; Patrick M.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A method of manufacturing and assembling a unitized seal for
installation in an annular space between outer and inner, relatively
rotatable members, said annular space being bisected widthwise by a
central imaginary cylinder and bisected lengthwise by a central imaginary
plane perpendicular thereto, said method comprising,
providing an outer, generally channel-shaped casing with an annular web
extending radially inwardly past said bisecting cylinder and a cylindrical
seal wall extending in one axial direction from said annular web to a
terminal edge, said terminal edge having a predetermined radial thickness,
providing an inner, generally channel-shaped casing with an annular web
extending radially outwardly past said bisecting cylinder and a
cylindrical seal wall substantially identical in length to said outer
casing seal wall but extending in the opposite axial direction from said
annular web to a terminal edge having a comparable radial thickness,
providing an integrally molded seal unit having, in a pre-assembly state, a
pair of inner and outer disks lying on said central plane and sized so as
to abut outer and inner casing annular webs respectively, said inner and
outer disks also being joined at a frangible seam lying on said central
bisecting cylinder, said inner and outer disks each having a pair of
axially oppositely extending converging seal lips symmetrically disposed
about said outer and inner casing seal walls respectively and defining an
annular opening of lesser radial width than said seal walls,
concentrically aligning said inner and outer casings with said seal unit
axially between, and
moving said aligned inner and outer casing axially together, thereby
pushing said inner and outer casing cylindrical seal wall terminal edges
axially into said respective annular openings and against said inner and
outer disks, fracturing said seam, and pushing said inner and outer disks
into abutment with said respective annular webs.
2. A method of manufacturing and assembling a unitized seal for
installation in an annular space between outer and inner, relatively
rotatable members, said annular space being bisected widthwise by a
central imaginary cylinder and bisected lengthwise by a central imaginary
plane perpendicular thereto, said method comprising,
providing an outer, generally channel-shaped casing with an annular web
extending radially inwardly past said bisecting cylinder and a cylindrical
seal wall extending in one axial direction from said annular web to a
terminal edge, said terminal edge having a predetermined radial thickness,
providing an inner, generally channel-shaped casing with an annular web
extending radially outwardly past said bisecting cylinder and a
cylindrical seal wall substantially identical in length to said outer
casing seal wall but extending in the opposite axial direction from said
annular web to a terminal edge having a comparable radial thickness,
providing an integrally molded seal unit having, in a pre-assembly state, a
pair of inner and outer disks lying on said central plane and sized so as
to abut said outer and inner casing annular webs respectively, said inner
and outer disks also being joined at a frangible seam lying on said
central bisecting cylinder, said inner and outer disks each having a pair
of axially oppositely extending converging seal lips symmetrically
disposed about said outer and inner casing seal walls respectively and
defining an annular opening of lesser radial width than said inner and
outer casing seal walls,
concentrically aligning said inner and outer casings with said seal unit
axially between,
moving said aligned inner and outer casing axially together, thereby
pushing said inner and outer casing cylindrical seal wall terminal edges
axially into said respective annular openings and against said inner and
outer disks, fracturing said seam, and pushing said inner and outer disks
into abutment with said respective annular webs, and,
axially parting said casings sufficiently to withdraw said inner and outer
casing cylindrical seal wall edges axially from said inner and outer
disks, thereby leaving said inner and outer casting seal walls engaged
only with said converging sealing lips.
Description
This invention relates to unitized seals in general, and specifically to a
simplified method for making such a seal that provides multiple levels of
sealing contact.
BACKGROUND OF THE INVENTION
So called unitized seals are so named because they can be installed as a
unit in the annular space between a pair of relatively rotatable members,
such as bearing races. Each of a pair of nested, coaxial metal casings is
press fit to one bearing race, while enclosed internal rubbing seals
provide sealing contact. Most older designs mold the seals directly to the
stamped casings. This requires holding the casings in a mold while the
elastomer seal lips are injection molded to and around some part or edge
of the casing. This molding step is somewhat difficult to control, since
the stamped metal casings do not always perfectly match the shape of the
mold cavities in which they are held.
A newer type of unitized seal avoids the seal molding step by using sealing
disks precut from flat sheets of polytetrafluoroethylene (PTFE) material,
which are separately glued or otherwise bonded to the casings. Potentially
lower seal torque or friction is possible with PTFE disks, because of the
slippery nature of the material.
A problem faced by both types of seals, integrally molded and PTFE disk
type, is the running eccentricity that bearing races are subject to, which
continually widens and narrows the annular space between the seal casings
mounted to them. Running eccentricity continually compresses and relaxes
the seal lips. This exacerbates the stress in a seal, especially when the
edge of the lip is bent back sharply at the line of sealing contact.
A seal design of the PTFE disk type is shown in co-assigned U.S. Pat. No.
5,201,533. There, two oppositely facing disks of seal material make four
separate areas of continual sealing contact, which alternate in
orientation. Therefore, despite any running eccentricity, two of the four
alternating areas of sealing contact are always increasing their pressure
when the other two are decreasing. The seal is manufactured by cutting the
two disks, gluing or otherwise securing them to the casings in a radially
overlapping fashion, pushing the casings axially together, beyond their
ultimate, installation position spacing, and then pulling them back.
There may be circumstances where an elastomer type seal that had the same
level of sealing integrity would be useful, provided a method for its
manufacture could be devised that still avoided the step of direct molding
to the casing. Ideally, such a method would be no more, and preferably
less, complicated than the method disclosed in U.S. Pat. No. 5,201,533.
SUMMARY OF THE INVENTION
The invention provides a method for manufacturing an elastomer type
unitized seal that has four alternating areas of sealing contact, as does
the design discussed above, but in which the elastomer seal lips are all
molded separately as part of an integral unit, not molded directly to the
two casings. Furthermore, the assembly method is simpler, in that no
assembly steps beyond just pushing the casings together is needed.
In the embodiment disclosed, outer and inner channel shaped stamped casings
have axially spaced annular webs and radially spaced, equal length
cylindrical seal walls. The terminal circular edges of each seal wall
faces the center of the opposed web. Therefore, if pushed axially
together, the terminal edge of each will bottom out simultaneously on the
web of the opposite casing. The radial thickness of the sealing walls of
the casings is a known, uniform quantity.
In its pre-installation, free molded state, the molded seal unit has two
pairs of frustoconical, converging seal lips, extending in opposite
directions from inner and outer disks and located so as to symmetrically
overlap a respective cylindrical seal wall. The converging lips do not
touch, but are open to a degree just less than the radial thickness of the
casing sealing walls. The inner edges of the disks are initially molded
together, in a plane, at a thin, circular seam.
To assemble, the casings are aligned concentrically, with the molded seal
unit axially between, and then pushed axially together. The elastomer
portion of the seal assembly essentially self installs as this is done.
The opposed sealing walls insert themselves between the two pairs of
sealing lips, then bottom out on the disks, shearing the seam. Ultimately,
the parted halves of the seal unit are pushed tightly into the opposed
casings, abutted with the casing webs, and then the casings are withdrawn
back to their installation spacing. The inner and outer sides of the
sealing walls are then each continually engaged with a seal lip.
DESCRIPTION OF THE PREFERRED EMBODIMENT
These and other objects and features of the invention will appear from the
following written description, and from the drawings, in which:
FIG. 1 is a cross section through a vehicle wheel bearing incorporating the
seal of the invention, with the seal beside, prior to installation;
FIG. 2A is a cross section through a pair of molds;
FIG. 2B is a detail of one mold;
FIG. 3 shows the molds closed;
FIG. 4 shows the molds opened with the modular molded seal unit between;
FIG. 5 shows the casings concentrically aligned, with the seal unit
between;
FIG. 6 shows the casings in their installation position, with the seal unit
to the side;
FIG. 7 shows the casings being initially pushed together;
FIG. 8 shows the casings pushed farther together;
FIG. 9 shows the casings pushed completely together, with the modular unit
sheared in half and the two halves fully embedded into the casings; disks
in a slightly deformed condition;
FIG. 10 shows the casings being pulled back to their installation position;
FIG. 11 shows the seal installed between the bearing races.
Referring first to FIGS. 1 and 11, a vehicle wheel bearing includes two
relatively rotatable members, an outer race 12, which surrounds a coaxial
inner race 14 to form an annular space therebetween. To create a
convenient reference frame, the annular space is bisected both by an
imaginary cylinder indicated at the dotted line C, and a plane
perpendicular thereto, labeled P. A unitized seal made according to the
invention, indicated generally at 16, is installed between the races 12
and 14. In fact, two would be installed, one on each side, but only one
need be described. Seal 16 blocks an exterior area from an interior area,
and is intended to keep the two separate, although some exchange in either
direction is inevitable, and can only be minimized.
Referring next to FIGS. 5 and 6, two of the three basic components of seal
16 are described in detail. Two casings, an outer casing indicated
generally at 18 and an inner casing indicated generally at 20, are each
channel shaped, or C shaped, in cross section. Each is stamped from steel
or other thin metal stock, with a uniform thickness. Outer casing 18
includes a longer cylindrical installation wall 22, a shorter, radially
spaced cylindrical seal wall 24, which faces axially outwardly, and an
annular web 26 that interconnects them. Inner casing 20 is the mirror
image of 18 about C and P, with an equal length cylindrical installation
wall 28 and equally shorter seal wall 30 that faces axially inwardly, and
an interconnecting annular web 32. The casings 18 and 20 are shown in
their ultimate installation position, concentrically aligned, and with a
total, web to web axial spacing S. The elastomer part of the seal, a
modular unit 34, is shown to the side for size comparison. In the
installation position, the oppositely extending seal walls 24 and 30 lie
on opposite sides of C, and their terminal edges face the radial centers
of, but do not touch, the opposed webs 32 and 26 respectively. Those edges
can be sharpened slightly, if desired, but would not be given a knife
edge.
Still referring to FIGS. 5 and 6, the only other basic component of seal 16
is the seal unit 34, which is integrally molded in a manner more fully
described below. It's dimensions and shape in the free molded, pre
installation state shown can best be described in terms of the same
reference frame as the casings 18 and 20, as well as by reference to the
casings 18 and 20 themselves. Unit 34, in general, consists of two
oppositely facing, open annular troughs joined at a frangible, central
circular seam 36. More specifically, radially inner and outer disks 38 and
40 lie on the central plane P, and to either radial side of the central
cylinder C. Inner disk 38 has an inner radius R.sub.1 slightly smaller
than the interior surface of inner casing installation wall 28, while
outer disk 40 has an outer radius R.sub.2 slightly larger than the
interior surface of outer casing installation wall 22. Therefore, inner
disk 38 is the right size and shape to abut the radially inner portion of
inner casing web 32, while outer disk 40 is abuttable with the radially
outer portion of outer casing web 26. A pair of converging, frustoconical
lips 42 extend axially inwardly from inner disk 38, subtending a shallow
angle of approximately thirty degrees. The inner seal lips 42 are best
defined in relation to the outer casing seal wall 24. Specifically, they
are symmetrically disposed to either side of seal wall 24, with an
effective axial length L that is longer than wall 24, but still shorter
than the casing installation spacing S. The seal lips 42 do not touch, but
instead present a narrow annular opening with a radial width W just less
than the thickness of seal wall 24. Likewise, a similar pair of
converging, frustoconical lips 44 extend axially outwardly from outer disk
40, defined in the same fashion relative to the inner casing seal wall 30.
Therefore, the two pairs of seal lips 42 and 44 are identical but for the
radii at which they lie. These dimensional relationships of the various
parts of the seal unit 34 and the casings 18 and 20 cooperate in the
assembly method for seal 16 described below.
The initial steps in the manufacture of seal 16, obviously, would be the
manufacture of the three basic components, the casings 18 and 20, and the
seal unit 34. The casings 18 and 20 are simple stampings, like those is
standard unitized seals. Therefore, their manufacture need not be
detailed, since it would follow standard stamping technique. However,
since the assembly process involves no direct molding of any elastomer to
the casings 18 and 20, nor gluing or other separate securement of a seal
member, this does allow the casings 18 and 20 to have the simplest cross
sectional shape possible. The cross section comprises two cylinders and
one annular web only, with no inherent radial overlap of any of its outer
surfaces, and with no holes or out turned edges needed for molding or
gluing purposes. Therefore, the casings 18 and 20 are also amenable to
being molded of hard nylon or other suitable material by a simple, axial
draw technique, if so desired.
Referring next to FIGS. 2A through 4, the manufacture of the third basic
component, seal unit 34, is described. Seal unit 34 is not as simple a
part as the casings 18 and 20, since it does have radial overlap of the
seal lips 42 and 44 with the disks 38 and 40. Therefore, more detail of
its manufacture is illustrated. Unit 34 is formed between a pair of molds,
indicated generally at 46 and 48. Each is machined with a cavity that
matches the outer surface of the left and right outer surfaces
respectively of the unit 34. The cavities would be difficult to machine
integrally into a solid mold, especially that part of the cavity that
corresponds to the seal lips 42 or 44. Therefore, it would be more
practical to build up a compound mold out of separately machined sections
that were later bolted together. As seen in FIG. 2B, one solution would be
to machine a separate insert with a rim 50 having a dove tail shaped cross
section, with a shallow angle alpha that corresponds to the angle
subtended between the seal lips 42. The rim 50 and separate sections 52
and 54 are simple to machine separately, with no thin concavities or
complex surfaces. Rim 50 is then bolted between two main mold sections 52
and 54 to produce the mold 46. Mold 48 would be built up in similar
fashion. Unit 34 is then injection molded between the closed molds 46 and
48 in conventional fashion, as shown in FIG. 3, of a suitable commercially
available seal elastomer. Finally, the molds 46 and 48 are parted, and
unit 34 ejected, as shown in FIG. 4. Conventional ejector pins, not
illustrated, would push the outer surfaces of the disks 38 and 40 away
from the molds 46 and 48, thereby isolating the central seam 36 from
stress. The lips 42 and 44 themselves would be flexible enough to be
withdrawn without damage as the ejector pins pushed the disks 38 and 40
out and away from the molds 46 and 48.
Referring next to FIGS. 7 through 10, the actual assembly of seal 16 is
illustrated. The casings 18 and 20 are first aligned concentrically with
each other, with the seal unit 34 between, and with the edges of the seal
walls 24 and 30 at or just between the openings between the pairs of lips
42 and 44 as shown in FIG. 7. This alignment could be done in a fixture or
jig, or could be done by a manual operator who simply inserts the edges of
the seal walls 24 and 30 simultaneously between the seal lips 42 and 44.
Doing that alone will sufficiently align the casings 18 and 20 with the
unit 34. Then, as shown in FIG. 8, the casings 18 and 20 are pushed
axially together, which will bring the edges of the seal walls 24 and 30
against the disks 38 and 40 respectively. Next, the casings 18 and 20 are
pushed axially together as far as possible, which pushes the terminal
edges of the seal walls 24 and 30 through the plane P and axially past one
another. This shearing action tears the seam 36, dividing unit 34 in two.
Simultaneously, the outer edges of the disks 38 and 48 are dragged
inwardly along the inner surfaces of the casing installation walls 28 and
22 respectively. Ultimately, as seen in FIG. 9, the disks 38 and 40 abut
the inner surfaces of the webs 32 and 26 respectively, where they are
maintained in place by the frictional interference of the outer edges of
the disks 38 and 40 with the inner surfaces of the installation walls 28
and 22. The pairs of seal lips 42 and 44 are deformed slightly from their
symmetrical position. Finally, as shown in FIG. 10 the casings can be
parted, to the FIG. 10 position, or at least far enough to pull the edges
of the seal walls 24 and 30 away from the disks 38 and 40. Reparting the
casings 18 and 20 is not as critical an assembly state, since installing
the seal 16 will accomplish the same effect, but it does take some stress
off of the seal lip pairs 42 and 44 before installation, allowing them to
flex back almost to their free state position.
Referring next to FIG. 11, the installed position of seal 16 is
illustrated. The actual installation would be conventional, and is not
shown. A suitable tool would push axially inwardly on both the edge of
outer installation wall 22 and the inner casing web 32 until they were
flush with the outer faces of the races 12 and 14. In the installed
position, there is insignificant axial overlap between the two seal walls
24 and 30. However, the effective length L of the two pairs of seal lips
42 and 44, being intermediate the length of the walls 24 and 30, but less
than S, is sufficient to assure that they axially overlap the seal walls
24 and 30 without rubbing on the webs 26 and 32. In addition, the free
state width W described above assures that there are four lines of sealing
contact maintained between the two pairs of seal lips 42, 44 and the
respective seal walls 24 and 30 that they axially overlap. The shallow
angle of the seal walls 24 and 30 relative to the seal lips 42, 44,
creates less stress at the points (or lines) of contact than is the case
with a disk shaped seal. (A seal disk is basically perpendicular to the
cylindrical member that it contacts, and so has its edge bent back
sharply, nearly 90 degrees, from the plane of the disk.) That same spatial
relation makes for less stress if there is significant whirl or
eccentricity between the casings 18 and 20. In that case, the seal lips 42
and 44 would bend up or down only slightly at their juncture with the
disks 38 and 40 as the seal walls 24 and 30 orbited off axis, and the
stress would not be taken all at a sharply bent back edge, as in a disk
seal. Furthermore, the spatial relation of the sealing lips 42, 44 and
seals walls 24, 30, the fact that they are radially interleaved with a
shallow relative angle and significant axial overlap, enhances sealing
effectiveness in another way. A very tortuous nature potential ingress or
egress path is created. As shown by the sinuous line in FIG. 11, to get in
or out through the annular space between the races 12 and 14, foreign
matter would have to traverse an extremely meandering path around and
between the interleaved members. In conclusion, the same structural
inter-relationships that allow for the simplified assembly process also
yield an improved sealing performance.
Variations in the assembly steps illustrated are possible. Rather than
squeezing the unit 34 between the two casings 18 and 20 simultaneously,
the unit 34 could first be partially installed to one casing or the other.
For example, the seal lips 42 could be inserted over seal wall 24, just so
far as to not tear seam 36, which would self fixture unit 34 and casing 18
in alignment. Then, the other casing 20 could be pushed in place. Or,
conceivably, the assembly and installation process could be combined, by
first installing outer casing 18 alone to outer race 12, but only
partially, leaving the installation wall 22 protruding partially from the
face of outer race 12. Then, the seal lips 42 could be inserted over seal
wall 24, as described above, so that the outer race 12 would serve as an
alignment fixture for both outer casing 18 and unit 34. Then, inner casing
web 32 could be pushed inwardly to its FIG. 11 installed position with a
tool that cleared the protruding outer installation wall 22. Doing so
would take the components through the same relative motions as shown in
FIGS. 8 and 9, shearing the seam 36 and embedding both disks 38 and 40
fully within the casings 20 and 18. Finally, the protruding installation
wall 22 could be pushed home to its FIG. 11 position. However as the
assembly and installation steps are ordered and carried out, the spatial
relationships of the sealing walls 24, 30 and the respective seal lip
pairs 42 and 44 yield the self alignment and self installation features
described, just from the axial squeezing motion of the casings 18 and 20.
Therefore, it will be understood that it is not intended to limit the
invention to just the embodiment described.
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